The extensive research and development into alumino-silicates has been highly successful and studies have turned to other materials that might lead to similar types of structures.
There are numerous classes of microporous silicates of interest in sorption, catalysis, and ion exchange, in which silicon is tetrahedrally coordinated through oxygen to numerous other metals in either tetrahedral or octahedral coordination. Primary amongst the former are the zeolites (see Barrer, "Hydrothermal Chemistry of Zeolites", Academic Press (1982) for a review), and amongst the latter, the clays (see Brown and Brindley, Clays and Clay Minerals, Min. Soc. (London), (1978), for a review). Whereas the zeolites are characterized by three dimensional covalent bonding the clays comprise sheets covalently bonded within the sheet and weakly ionically bonded between the sheets. In some cases, when the sheets are electrostatically neutral, as in talc or kaolin, the sheets are held together by weak van der Waals forces. Other classes of similar structures include the sheet like silicic acid materials (e.g., Legally, Adv. Colloid and Interface Sc., Vol. II, p. 105 (1979)) and the many sheet materials rendered three dimensional by various pillaring reactions (see Vaughan, Amer. Chem. Soc. Symp. Ser. 368, p. 308 (1988) for a review).
Within each of these major families of materials are many subgroups. The three dimensional tetrahedrally coordinated structures now include a large number of metallo-phosphates (see Wilson, Flanigen et al, Amer. Chem. Soc. Symp. 398, p. 329 (1989); Proc. 7th Intl. Zeol. Conf., Elsevier Press (Tokyo), p. 103 (1986), for recent reviews), silicas and various modified silicas. The latter two include clathrasils (various SiO.sub.2 analogues of the ice clathrates) and zeosils (SiO.sub.2 analogues of various zeolite structures). This terminology has been reviewed by Liebau et al, Zeolites, Vol. 6, p. 373 (1986). Much recent work has focused on many metal modifications of the zeosils. An unusual and unexpected characteristic of these materials is a high concentration of "internal" hydroxyl groups (Woolery et al, Zeolites, Vol. 6, p. 14 1986)) which seem to readily react with numerous metal cations (U.S. Pat. No. 4,576,805; Eur. Pat. Appl. 0134,849; UK Pat. Appl. GB 2,024,790A). However, the metal content of such materials is usually less than about 1 to 2% wt. Various other methods of metal substitution into conventional zeolites could be envisioned by manipulating established methods of dealumination, such as high temperature gas phase reactions (Fejes et al, React. Kinet. Catal. Letters, Vol. 14, p. 481 (1980); Beyer et al, Stud. Surf. Sci. Catal; Vol. 5, p. 203 (1980), Elsevier Press), aqueous ammonium metal fluoride treatments (Breck and Skeels, Proc. 6th Intl. Zeol. Conf., p. 87 (1984), Butterworths), or non-aqueous solvent "exchange" treatments (Intl. Pat. WO 88/01254), and substitutions under hydrothermal conditions. Whilst all of these methods may involve tin substitution into zeolite or zeolite like tetrahedral frameworks, they are distinctly different products from those of the instant invention, both in structure and composition (i.e., the level of tin included in the structure).
The many ways of coordinating or interlinking tetrahedra, octahedra or a combination of the two have been considered by several authors (e.g., A.F. Wells, "Structural Inorganic Chemistry", 5th Ed., Oxford Univ. Press, Ch. 5 (1984)). Although there are many thousands of possible structures in a strictly mathematical sense, the reality is that only a relatively small number of them exist in nature or can be synthesized in the laboratory. Four different general examples of such structures are shown in FIG. 1. The instant invention is concerned with materials in which silicon is in tetrahedral coordination and tin is in octahedral coordination, said materials having unique and definitive structures as identified by their characteristic x-ray diffraction patterns.
Oxide and mixed oxide crystalline structures with tin are well known in the literature, and in these cases all metals are octahedrally coordinated. Examples of these include SnO.sub.2 itself (cassiterite), Li.sub.8 SnO.sub.6 (Tromel, Zeit. Anorg. Allg. Chem., v. 368, p. 248 (1969)) and Li.sub.2 SnO.sub.3 (Lang, ibid, v. 348, p. 246 (1966)) in addition to numerous temarz tin oxides (Clayden et al, J. Chem. Soc. Dalton, p. 843 (1989)) and rare earth stannates (Grey et al, J. Amer. Chem. Soc., v. III, p. 505 (1989)). In other materials tin is octahedral and other metals are tetrahedral, as in the minerals:
Eaherite A. A. Kossiahoff Am. Miner. 1976, v. 61, p. 956. PA0 Mizerite I. E. Grey Am. Miner. 1979, v. 64, p. 1255. PA0 Malayaite J. B. Higgins Am. Miner. 1977, v. 62, p. 801. PA0 Stohesite A. Vorma Miner. Mag. 1963, v. 33, p. 615. PA0 Sorensenite J. M. - Johansen Acter Chyst. 1976, V. B32, p. 2553. PA0 V. N. Rudenko et al, Mineral. Zh. 1983, 5, 70. PA0 F. K. Larsen et al, Acta Chem. Scand. 1967, 21, 1281. PA0 N. V. Zayakina et al, Dokl. Akad. Nauk SSSR 1980, 254, 353. PA0 A. N. Safronov et al, Dokl, Akad. Nauk SSSR 1980, 255, 1114. PA0 A. N. Safronov et al, Dokl. Akad. Nauk SSSR 1983, 269, 850. PA0 I. V. Rozhdestvenskaya et al, Mineral. Zh. 1985, 7, 78. PA0 V. V. Gorokhovskii et al, Izv. Akad. Nauk SSSR, Neorg. Mater. 1971, 7, 2033. PA0 I. Y. Nekrasov, Dokl, Akad. Nauk SSSR 1973, 212, 705. PA0 I. V. Nekrasov et al, Dokl. AKad. Nauk SSSR 1977, 232, 909. PA0 I. A. Nekrasov et al, Fiz.-Khim. Petrol. 1978, 8, 193. PA0 I. Y. Nekrasov et al, Dokl. Akad. Nauk SSSR 1978, 243, 1286. PA0 I. Y. Nekrasov et al, Dokl. Akad. Nauk SSSR 1981, 261, 479. PA0 G. T. Desai and D. R. Baxi, Indian J. Tech. 1978, 16, 201. PA0 A. N. Christiansen, Acta. Chem. Scand., 24, p. 1287 (1970).
Similar synthetic materials of this type are extensive (e.g.)
However, in none of these cases are the materials of this invention reported, nor would one expect to make them using the methods of synthesis used by those researchers.
In addition to the crystalline materials detailed above are many amorphous or gel materials made by cogellation of a stannate with a silicate. In some cases these comprise true gels, but in other cases they comprise tin hydroxide precipitated in a matrix of silica gel. Numerous of these have been evaluated as ion exchangers (e.g., U.S. Pat. No. 4,329,328) and catalysts (Tanabe, "Solid acids and bases", p. 71, Kodansha Press (1970)).